The present invention relates to a frame-supported pellicle for photolithography or, more particularly, to a frame-supported pellicle which is a device consisting of a rigid frame and a thin transparent film of a plastic resin spread over and adhesively bonded to one end surface of the frame in a slack-free fashion and used for dustproof protection of a photomask in the photolithographic patterning works involved in the manufacturing process of fine electronic devices such as ICs, LSIs and the like.
As is known, the manufacturing process of fine electronic devices such as ICs and LSIs as well as liquid-crystal display panels and the like involves a photolithographic patterning work in which a patterned resist layer is formed on the surface of a substrate such as a semiconductor silicon wafer by pattern-wise exposure to light of a uniform photoresist layer through a pattern-bearing transparency called a photomask followed by the development of the patterned latent image. In view of the extreme fineness of the pattern to be reproduced, any smallest number of dust particles deposited on the photomask may cause a heavy decrease in the quality of the reproduced pattern consequently to affect the quality of the electronic devices manufactured thereby.
Although the patterning work above mentioned is performed usually in a clean room of which the atmospheric air is freed from floating dust particles as completely as possible, it is a difficult matter to ensure a perfectly dust-free condition of the photomasks even in a clean room of the highest class. Accordingly, it is a usual practice that the photomask is protected from falling dust particles by mounting thereon a frame-supported pellicle or, simply, pellicle, which is an integral device consisting of a frame, referred to as a pellicle frame hereinafter, of a rigid material such as an aluminum-based alloy, stainless steel, high-density polyethylene and the like and a thin, highly transparent membrane, referred to as a pellicle membrane hereinafter, spread over and adhesively bonded to one end surface of the pellicle frame in a slack-free fashion while the other end surface of the pellicle frame is coated with a pressure-sensitive adhesive so as to facilitate securing of the pellicle frame on the proper position of the photomask when the pellicle is mounted on the photomask.
Since dust particles fall and are deposited on the pellicle membrane which is apart from the photomask by the height of the pellicle frame when the frame-supported pellicle is mounted on the photomask, the dust particles on the pellicle membrane have no particular adverse influences against the rays of light focused at the photomask to minimize degradation of the quality of the reproduced pattern.
While the above mentioned pellicle membranes are conventionally made from various plastic resins such as nitrocellulose, cellulose acetate and the like having high transparency, several other plastic resins have come under practical use for the purpose in order to comply with the requirements for the pellicle membranes being upgraded year by year. For example, it is a recent trend in the photolithographic patterning work that the wavelength of the light used for the pattern-wise light-exposure is shorter and shorter than heretofore to give higher resolution of pattern reproduction required for the manufacture of electronic devices of increased fineness so that a proposal has been made for the use of an-amorphous fiuorocarbon-based special plastic resin as the material of the pellicle membranes in view of their high resistance to withstand the short-wavelength ultraviolet light which necessarily causes serious photodegradation of other conventional plastic resins for pellicle membranes. Even by setting aside the problem of their expensiveness, these fiuorocarbon-based plastic resins as a material of pellicle membranes have a defect that, as compared with membranes of conventional nitrocellulose, cellulose acetate and the like, the membrane thereof is subject to stretching under an external force so that the slack-free condition of the pellicle membrane on the pellicle frame is sometimes lost by air blowing conventionally undertaken in order to blow off dust particles deposited thereon.